[Hardly Sporting]

Hello,

I'm in the process of finishing my basement and have decided to go for a completely hidden sound system. I bought some Definitive Technology speakers but haven't found any in-wall subs that seem like a great deal. So, I figure I'll try my hand at building my own. Minor problem- I'm nearly to drywall so I need to work fast! I'm doing electrical so I could drag that out, but the wife would like me to finish eventually.

Since I have no idea what I'm doing, I figured I'd ask you fine folks a few questions. I searched but didn't find much on in-wall subs.

A few general notes- largeish, open room, approx. 750 square feet with 8.25' ceilings. The framing is steel, not sure if that has any impact on the project. I'm no audiophile or home theater buff, just want something that sounds decent and is hidden (function follows form for me). I'm an hobby woodworker so I have all the gear and such. My budget is about $400 - $500 including amplification (I have 1/2 MDF and wire already). That reasonable or way too low?

On to the questions:
1. Drivers- I'll need something low profile of course- I found these monoprice in-wall subs but they don't go very low, so am wondering if anyone has any recommendations on drivers that would work in a standard wall. My plan was to get 2 in an attempt to get decent performance while staying in budget. Monoprice Alpha In-Wall Speaker 10in Carbon Fiber 300W Subwoofer (each) - Monoprice.com
2. Enclosure- the monoprice ones don't call for an enclosure, but that seems strange to me. The options I've seen have tall, narrow boxes to enclose the speaker- seems like the way to go. My current plan involves a 4 inch deep (have a small amount of extra room behind the framing) 72 inch tall sealed enclosure made of 1/2 inch MDF. This would be mounted directly to the metal studs. Does this seem reasonable? Also, would the interior simply be a box or would you recommend any baffles or other internal structures- I'm assuming sealed is fine, or would a port be better? Should I fill the space with fiberglass or leave it open? This is the inspiration: https://www.digitalhomecreations.co...er-veneer-12-in-wall-subwoofer-1064595-175087
3. Other- any concerns with the metal framing? It's pretty flimsy, but does firm up with drywall attached. Anything else I've missed

Appreciate your time.

 

[smcmillan2]

Ok, I'll be that guy. You're never going to get good response with subwoofers unless you measured or have done the sub crawl. Most basic response.

In-wall subs require you measure from the MLP in my mind, no idea why someone would opt for those. There is no room for movement should the room/furniture change.

Why are you decided on in-wall subs? Other speakers can work well with slight adjustments, subwoofers are not in that realm.

 

[Hardly Sporting]

It's all about looks and floor space. I want decent sounding of course, but invisible is the goal.

I do have one spot I could pry do some sort of IB, but I'm concerned about damage to exposed drivers in the utility area

 

[(The Other) Colin Miller]

Since somebody has already done you the favor of telling you the most useful information you can get that you didn't want to hear.

I will follow up and say that if you're sincerely interested in any kind of playback quality, while the limitations of what you can do with the volume available with in-wall subs are one thing, if they are the best you're going to be able to sell or tolerate, so be it. But, if that is the case, most definitely verify that the locations chosen work well in the main listening area, with the furniture located, both in terms of which bay, but also how high, before you do any permanent installation. This may mean you just run a speaker cable to every bay you can possibly use and leave it in the wall, leave it loose in the wall, then borrow some subs as well as stools, ladders, or tie-down straps and hooks in the ceiling joists, to actually determine the optimal locations, and then retrofit them and perhaps do a little drywall patch.

If you take the standard 'custom install' approach, and simply put the subwoofers were you think they'll look good, or where some expert told you at a seminar would be the best location, or where the interior decorator points, you might get lucky, or you might end up with craptastic bass no matter how much money you throw into hardware, which would kind of suck, right?

 

[Hardly Sporting]

I appreciate the input - I'm taking an approach that will provide results worse than what I could get with other approaches, but I knew that up front. You're talking to a dude who's current best speaker is a Sonos. The smallest one. I think the key difference is that my system goals are different that most folks who bother to make their own speakers, I just want to enhance the sound a little- I'm not an enthusiast and the room isn't dedicated to theater. It's why my system budget is so low at a total of $2,500 and I have a hard and fast rule that it all will be invisible.

With that said- I can make an in-wall, or I could make something a little deeper at roughly 14.5 inches wide, 8 inches deep, and 60 inches tall. The downside is that I could put that in one, and only one, location. It doesn't seem terrible, it would be in a corner in the behind and to the right of the listening position. This would give me a pretty sizable enclosure at 3ish cubic feet, but a very strange layout and wouldn't be able to tune the location. Thoughts on the choice there?

 

[(The Other) Colin Miller]

Unless I absolutely knew that the single location capable of a larger enclosure was the best location, I would go for more location options with smaller enclosures. Plus, if you just leave wiring available, you can always retrofit more later, and the great thing about subwoofers, is that although adding more may or may not require a bit of work in terms of integration, depending on how picky and or lucky you are, you can often make up for deficiencies with volume, be they limitations of a single subwoofer's output vs. distortion/compression, or the room response improving by averaging or balancing how standing waves are driven.

Not having an enclosure is going to be a limitation, unless you build one into the wall, because a good chunk of your output is going to be cancelled by sheet rock flexure, unless you're using 3/4" birch or something similar, with the outer grain oriented horizontally across the bay.

If you build an enclosure, that goes into the wall, you also have to account for the thickness of the enclosure walls, and how that a affects the actual air volume available.

What might work well is simply to mount the driver to a 16" wide panel front baffle, even maybe a modular panel, so that in a bay you have the driver mounting panel, a bottom fill, and a top fill panel, and the fill panels can be of a few different sizes, made of birch or maple plywood, in that you can maximize internal volume but don't get the loss from baffle flexure, and they're a lot easier to build.

If I was in your position, I would...


Download REW, and kick them a few volunteer dollars as a thank you.

Order a MiniDSP UMIK-1 USB calibrated microphone.

Solicit suggestions for drivers that will work reasonably well (with a Qtc under 1.0 or so, though Qtc of 0.7 or so would be theoretically more ideal) and an F10 point of 30 Hz or lower, honest useable Xmax of 10mm or more, a cost that allows you to buy four of them, whatever that limit is, with the depth the allows you to do what you want.

On the depth issue, you mention that you have space behind the framing. You'll probably want to seal that on final installation to prevent the out of phase flexure of sheetrock from simply migrating to other bays. Also, in selecting drivers, some drivers have vents in the back that need a little bit of space to breathe, and also consider that the frame has some depth that if you don't account for it, means it must be mounted on top of, as opposed to flush with, the surface. You can get a little more mounting depth by cutting a spacer ring that sets the subwoofer a bit out.

I don't have any experience with drivers that will fit your needs, but if I was doing it, my first gander would be an SI 12" BM mkV, and start with one somewhere up front, play with REW and see what it does in different locations, either with the modular baffle idea (and for location testing you can just seal the baffles and bay with masking tape), or with a cheap unfinished temporary knock down enclosure like this one...

Home, or just slap something together with 3/4" whatever that's 12" by 12" by 12" or so. (specific to this driver).

From there, you're not looking for the best performance from your driver, you just want to look for rough changes in frequency response in the room. Use the REW software to do quick sweeps, measured at the main listening position, and go for the smoothest room response, not necessarily the deepest bass. If you can find a position with one subwoofer (and keep in mind that that position may involve variations in elevation), that doesn't give you any deep nulls, cool. If not, order another driver and continue testing iterations.

If cost was less of an object, I would say just order four drivers, and if one location works great, four will probably too, though you may have to play as you probably don't have enough air volume in a single bay to put them all next to each other.

After you determine where the subs go, install the baffles, permanently, with sealing, wiring,etc., and what not, and then put the drivers someplace safe while the rest of the sheetrock and mud and painting goes in.

the monoprice driver/bracket/baffle kits look attactive and handy, though my main concern with them is the listed 3mm of Xmax. That is incredibly low for a subwoofer. They might work well enough if your standard is a small sonos speaker, and will certainly be an improvement, and could be fine so long as you're not cranking anything, but it would make me hesitate and want to ask people like Chris Popovich (did I spell his name correctly, if not sorry) if he can think of anything both suitable and possibly more cost effective than the SI version I linked. That driver might work very well if one location works well, but 4 of them could get expensive given your budget. Still one, or maybe two, could possibly work remarkably well.

Once the room is finished, install the subs, and then grab a MiniDSP EQ to actually dial in the subwoofer curve you want. It is my personal bias that at that point, dialing in the phase response of the mains and the subwoofers is worthwhile as well, though that opinion can surely be debated.

 

[Hardly Sporting]

Thank you very much for all that info! I'll be downloading that software and getting a mic to do some fun playing around.

I found a driver that's pretty budget friendly and has 10mm of xmax- which seems pretty good for the design constraints- if you have time to look at it quick I'd much appreciate any input if I'm missing anything that makes it less than ideal: Home

It's a little deep, but I can cut out some insulation to provide more space behind the woofer if that would help. That would give me about 6 inches of total depth.

What comes to mind is that I can build in baffles for them in say 6 locations and seal those up with some 1/2 mdf. Once you build one, building a bunch more is trivial. Then, once drywall is up I can make a small enclosure like you mention and test them out at those locations to determine which was the best. Seems like I can get benefits of a decent seal and stiff baffle while providing at least some flexibility on location. I can also have room to add more with minimal effort. with these I'd probably start with two and then could add a couple more if I need more punch and the locations test out well.

Does that seem like a reasonable plan?

I can do my own research, but if you have any nice ideas for amplification that would be nice too

Thank you again.

 

[Charles Collins]

It's all about looks and floor space. I want decent sounding of course, but invisible is the goal.

I do have one spot I could pry do some sort of IB, but I'm concerned about damage to exposed drivers in the utility area

With invisible as the goal in mind, have you considered a low profile sub that could conceivably fit under the seating and be out of sight? Dayton Audio makes this one:

Home

One of the photos shows it underneath a couch. I have a similar 8” sub made by Monoprice that seems to do well paired with a couple of bookshelf speakers in a medium sized room.

Just throwing this out here in case you haven’t considered going this route...

 

[Hardly Sporting]

Those are cool. My concern would be how to get the wires to it. I don't have any furniture that we plan to place against a wall.

I'm doing built ins next to the TV, so I could put a sub in there, but I'm concerned about putting a sub in something like that cause it could rattle

 

[Charles Collins]

Those are cool. My concern would be how to get the wires to it. I don't have any furniture that we plan to place against a wall.

I'm doing built ins next to the TV, so I could put a sub in there, but I'm concerned about putting a sub in something like that cause it could rattle

You said this was in your basement. So I would assume you have a concrete slab floor and are planning to put a finished floor or carpet over it. Cutting a groove in the concrete and running some conduit and wires for an in-floor electrical power outlet and some audio signal wiring then patching the concrete is feasible. But I would make sure that you have adequate clearance under whatever furniture or seating that you have planned. It might be worth investigating the costs involved.

 

[(The Other) Colin Miller]

If you wanted to get wiring to your couch, you could also just put a 1/2" thick subfloor with channels cut, if that is cheaper than notching the concrete, though I would guess probably not. You could also do a platform, or just a platform between the couch and the nearest wall that will not need foot traffic, and put an end table on the short platform.

The drivers you selected, I think it short would work. They seem to be optimized for very very small enclosures, smaller than even a bay would provide, but that isn't necessarily bad, could even be good.

The result is that you get a very low Qtc of about 0.495, which means an early, but very gradual roll-off. The F3 cutoff point, which is your typical single index (and incomplete) description of the low end limit is only 62 Hz, which kind of sucks in itself, though that's really misleading, as it's falling so slowly, that with 10 dB of boost with the right shelving filter or linkwitz transform with a MiniDSP, you can have an anechoic F3 in the low twenties, which is pretty darn good. Also, depending on where your subwoofers are placed, and how they sum with each other at the main listening position, you may get some pretty significant room gain. My 4 12" subwoofers, based on measuring in-box TS parameters, have an anechoic F3 of 50 Hz and a Qtc of 0.5, which seems very much not a subwoofer, but in my room, by the luck of how they're set up to achieve the flattest response with the positions I have available, it worked out to be -4 dB at 8 Hz, before applying any EQ at all. I actually use an infrasonic filter to attenuate content below 20 Hz, though I still use EQ to boost above that for subjective effect, in general by about 6-7 dB for most movie playback.

We're still in the land of theory, so what actually happens is going to depend a lot on the room, and manufacturing variances of the drivers, but that's the best we can do until we actually get a sample of reality, so... back to theory...

You're still displacement limited in output, so you might not actually want that kind of extension to protect the excursion limits and get more available playback volume, which means simply adjusting your EQ curve, but you've got options...

You've likely got enough air in a bay to run two of them if you wanted (or retrofit a second later if you decide you need more).

That would raise the Qtc to about 0.55 (not much), which translates into a curve that means that you'd need more low end EQ boost to extend the response (about 12 dB for a 20 Hz F3), but it will raise your low displacement limits by about 6 dB.

The other thing is that the woofers are dual 4 ohm drivers, meaning that you'll likely want to run them in series for an 8 ohm load, which most amplifiers will work fine with, but can deliver more power into a 4 ohm load. If you've got multiple drivers, you wire the coils in series, and then run pairs of drivers in parallel, to give you 4 ohms. Lots of combinations, including running multiple locations with a single amplifier channel, though for reasons of control, tuning, alignment, etc., I would like to keep subwoofers that are at different distances to the main listening position on different channels for flexibility, but so long as they are wired separately at the equipment location, you can do what you want, when you want.

When you're playing with locations, I would say simply mount them backwards, so you don't have to dig out clearance for the motor before you decide that it's really where you want it.

That's all I've got for now. It's not the most expert advice you're can possibly get, even for the asking price, but it's still cheap, and you can have your money back if it doesn't work out for you.

 

[buggers]

Have you considered the BOSS platform?

 

[Hardly Sporting]

Colin- thank you so much for that ultra helpful response!

Looking at your modeling I think I like the idea of these drivers- I'm going to start with 2 and then see if I need more. I'll add the baffles in a bunch of locations now and that way installation will be easy.

With the 2 drivers, would you recommend putting them in the same bay or splitting them up in different parts of the room? I can put together the boxes to test things out, but was just wondering what your gut feeling was there

Along those lines, I could make these into sealed enclosures pretty easily, or just seal up the bays, thought I doubt that would be a perfect seal. Do you think that making a size optimized enclosure is worth the effort? I worry a bit about the rigidity of the steel studs, so I'll be doing a lot of reinforcement on the selected bays anyway.

Since this room isn't a dedicated theater, I'd rather not have things installed on the floor in case we change up furniture, clear things out for games, and other assorted things.

I'm getting the gear to do some testing as well, just wanna lay the groundwork

Thank you again

 

[(The Other) Colin Miller]

With the 2 drivers, would you recommend putting them in the same bay or splitting them up in different parts of the room? I can put together the boxes to test things out, but was just wondering what your gut feeling was there.

my gut feeling is to not answer the question, as whatever it is is probably wrong.

The simple answer is try and see. the accurate answer is that it depends, on a lot of things, and while sometimes you can make predictions, I wouldn't rely on anything for sure. Experts disagree.

As a starter, I would recommend reading up on the work of Floyd Toole, Ethan Winer, and Barry Ober.

https://www.harman.com/documents/LoudspeakersandRoomsPt3_0.pdf

Ethan Winer

Acoustics FAQ

ethanwiner.com

Soundoctor - all about subs

Links provided are certainly not the entirety of useful information, either offered by those individuals, or others, but are a good start and basis for further discussion, and will give you the beginning of getting a handle on what you can use to figure out your approach, and tailor modifications and adaptation depending on the results, but you're basically looking at how the subwoofer location interacts with standing waves, the acoustic behavior of the room, which includes, but is not limited to standing waves, and the phase behavior of the subwoofer, in relation to both how location interacts with the phase of standing waves, and how that phase interacts with the main speakers at the crossover region, which in my experience is largely neglected to the detriment of what is often referred to in this forum at least as subwoofer 'midbass'.

On top of the information provided by experts, I have my own opinions as to how to use that information, and where perhaps I differ from some of their assessments of data and theory, or to how to best implement that, but that is also based on my own experience and priorities, and I expect it will not apply universally, and instead of simply spouting them to you, if you're interested, read up and then discuss.

Along those lines, I could make these into sealed enclosures pretty easily, or just seal up the bays, thought I doubt that would be a perfect seal. Do you think that making a size optimized enclosure is worth the effort? I worry a bit about the rigidity of the steel studs, so I'll be doing a lot of reinforcement on the selected bays anyway.

While the seal of the enclosed air behind the driver will definitely make a difference in driver response, that variation is really going to be largely offset by what you end up doing to the low frequency EQ extension, and that will depend on what response you decide on, and what it takes to get there, so the EQ will largely compensate for what you do with the internal structure. The only really critical thing is that you have a rigid baffle and seal between the air behind the driver and the front of the driver. You can certainly build an enclosure, but that also takes up a fair amount of volume. You could simply seal and line the sides over the steel studs (with MDF or whatever), particularly if they will have holes, and that won't lose you much volume, because those sides are thin slices, and don't involve that much material. If you make a full enclosure that goes inside with 3/4" walls, instead of 4" of depth, you'll have 2 1/2" of depth of available volume, which does significantly reduce the air volume. I don't know if that's what you're talking about.

It sounds fun, much luck, and enjoy the experience and share what you find,

Edit:
Oh, I assumed you knew, but just in case you didn't know, you want some kind of absorption material in the space of the woofer. I don't know if your building code will be cool with polyester fiber, but you could put certainly regular old fiberglass, or rock wool if it's the light stuff. I don't think you want to use the soundproofing variety, even if it's meant for 'acoustics'. I think it's meant mostly for preventing sound from traveling through the wall, but I put some in some enclosures and it jacked up the system resonance frequency a little bit compared to regular fiber fill.